The present invention relates to molding of articles of manufacture, and more particularly relates to methods and apparatus for separating excess, unwanted lens material from a mold surface. The present invention has particular application to the production of molded ophthalmic lenses such as contact lenses and intraocular lenses.
Static cast molding of contact lenses is known. See, for example, U.S. Pat. No. 5,466,147 issued to Bausch and Lomb Incorporated, the entire reference of which is incorporated herein by reference. A single mold unit for making a single lens comprises a female mold section having a concave optical surface and a male mold section having a convex optical surface. The female and male mold sections are complimentary shaped and are brought together to form a lens-molding cavity between the facing concave and convex optical surfaces of the female and male mold sections, respectively.
Although less popular than full cast molding, forming lenses by spin-casting is also known where lens material is deposited into a female mold section and spun to form the anterior surface of the lens. The posterior surface is then formed by a lathe cutting operation. In this method of lens manufacture, excess material may also form on the female mold section with may require removal prior to lens release from the mold.
The basic process for cast molding a lens is as follows. A quantity of liquid lens material is dispensed into the concave optical surface of the female mold section and the male mold section is seated upon the female mold section with the concave and convex surfaces thereof facing one another to form a lens-shaped mold cavity. The joined female and male mold sections form a single mold unit which is subject to a curing cycle (e.g., by thermal or UV radiation) thereby causing polymerization of the lens material in the mold cavity. Once the lens material has cured, the male and female mold sections must be separated to retrieve the cured lens.
The opening or release of the mold sections must be carried out in a manner which will not harm the delicate lens. Once the lens has polymerized in the mold cavity, the lens and any excess lens material will have an adhesive bond to the opposite concave and convex mold surfaces. Thus, the release of the male mold section from the female mold section must be of a force strong enough to break the adhesive bond of the lens and excess lens material to the opposing mold surfaces, yet not so forceful or haphazard that the optical surfaces of the lens are harmed by the release process. Should the lens crack or be otherwise damaged during the mold release process, the lens must be scrapped, thereby lowering the output yield and increasing manufacturing costs.
Once the mold sections have been separated, the lens will adhere to one of the mold surfaces and must therefore be released from the mold section on which it is retained. Both wet and dry release methods of lens release have been proposed in the prior art. In wet lens release methods, an aqueous solution is used to wet the hydrophilic lens which absorbs water and swells, causing the lens to separate from the mold surface. In dry release methods, the lens is removed from the associated mold surface while still in the dry state. The adhesive bond between the lens and mold surface is broken, usually by application of a force to the mold body, for example by squeezing or pressing against the non-optical surface of the mold to move the mold surface relative to the rigid lens. Once the adhesive bond has been broken, the lens is retrieved, for example by a vacuum picking tool.
To ensure that the mold cavity is completely filled with the liquid lens material during the molding process described above, the quantity of liquid lens material dispensed in the female mold section is purposely greater than that needed to form the lens. When the male mold section is seated upon the female mold section, the excess liquid lens material is expelled from the mold cavity. This excess liquid is typically held in a reservoir, groove or flange surrounding the mold cavity and is cured along with the lens. The cured excess material is typically referred to as a xe2x80x9cmonomer ringxe2x80x9d or xe2x80x9chema ringxe2x80x9d in the contact lens art depending on the specific lens material used. The term xe2x80x9cmonomer ringxe2x80x9d will be used herein for convenience, although it is understood this term is used broadly herein to cover any type of lens material employed.
During mold separation, the monomer ring will usually adhere to one of the mold sections with the monomer ring usually retained in the female mold section along with the lens. Should the lens be released and removed from the female mold surface without prior removal of the monomer ring from the reservoir, the lens edge will likely be damaged due to interference with the monomer ring. This problem is illustrated in prior art FIG. 5C herein. Presence of the monomer ring can also interfere with downstream processes and machinery. It is thus desirable to release and remove the monomer ring from the female mold section prior to release and removal of the lens therefrom.
Various monomer ring removal processes have been employed in the prior art, none of which has proven very satisfactory.
The present invention is directed toward a method and apparatus for removing a monomer ring from the mold section to which it is adhered following mold separation. The monomer ring may be located on a flange, groove, or reservoir surrounding the molding surface.
The present invention is particularly useful for removing cured excess material formed in contact lens or intraocular lens molds, although it is equally applicable to other molds requiring removal of excess material. Excess material in an ophthalmic mold, also known as a monomer ring, can cause damage to the molded lens if the monomer ring is not released and removed from the mold section prior to release and removal of the lens from the mold section.
In the preferred embodiment, following the curing stage, the mold is opened and the mold section to which the monomer ring and lens are adhered is presented for removal of the monomer ring while leaving the lens unharmed and intact. The monomer ring is removed by a plurality of members (e.g., pins or blades) which descend from a location directly above the mold section to pierce the monomer ring but not so deep as to penetrate the mold section. The pins then rotate which shears the monomer ring free of the mold section. The pins are then raised, carrying the monomer ring along with it for disposal. Thereafter, the now monomer ring-free mold section having the lens adhered thereto is transferred to a lens release station and further downline processing as desired. As used herein, the word xe2x80x9cpiercexe2x80x9d is broadly interpreted to mean any device or member capable of engaging and moving the monomer ring relative to the mold.